Belt tensioners serve for eliminating a belt slack in the case of strong deceleration so that the vehicle occupant can more quickly take part in the overall deceleration of the vehicle. A buckle tensioner includes a flexible tension transmitting means, for instance a steel cable, to which a belt buckle of a seat belt is fastened. The tension transmitting means is mounted to a drive unit and is deflected toward the belt buckle via a deflection fixed to the vehicle. When activating the drive unit, the latter pulls the tension transmitting means through the deflector so that the belt buckle fastened to the tension transmitting means is pulled in the direction of the deflection. The displacement of the belt buckle and thus the pull-in of the belt strap here correspond to the travel of the drive unit. The limited mounting space in a vehicle confines the tensioning distance of the drive unit.
It is the object of the invention to provide a belt tensioner permitting a longer travel of the belt buckle and thus a belt tensioning over a longer distance, a compact construction notwithstanding.